A British study assessing whether Covid vaccines can disrupt periods may not find anything because it is too small, scientists say.
Reproductive experts based at Imperial College London are currently monitoring the menstrual cycles of 250 women before and after inoculation.
But lead researcher Dr Victoria Male said the tiny number of participants means the study won't pick up a potential link unless it is 'really common' — affecting more than one in ten women.
To prove a link, scientists need to untangle normal period changes from those which may have been sparked by inoculations.
But because period issues, which are often transient, affect approximately one in ten women every year, thorough investigations are needed to spot whether the jab may really be to blame.
Nearly 36,000 women have reported experiencing period issues after receiving the Covid vaccine. But experts fear this is only the tip of the iceberg because many women who experienced the changes likely did not report them.
Period issues reported after getting the Covid vaccine include heavy bleeding, missing periods, and periods being earlier or later than usual.
Some postmenopausal women have also said they experienced vaginal bleeding after being vaccinated.
Dr Male said they aimed to establish whether there was a link and, if there is, get this listed as a side effect of Covid vaccines to allay any concerns over being jabbed.
She said that by 'brushing it under the rug' regulators were not acknowledging fears over jabs.
Some 35,700 women have now come forward to say their periods were disrupted after getting a Covid vaccine, it was revealed (stock image)
Experts only honed in on a connection between the AstraZeneca vaccine and blood clots after noticing more cases than expected among recipients.
And the same happened for Pfizer's jab when it was linked to heart inflammation, or myocarditis.
But both issues were spotted in data collected from real-world roll outs because the complications were rare enough to disentangle the link.
Britain's medical regulator has refused to accept or deny a link to disrupted cycles, and says most menstrual problems appear to be 'transient' in nature.
But period issues have previously been linked to other vaccines, such as the HPV jab.
However, there is no evidence that Covid vaccines affect fertility, top doctors insist.
Dr Male told MailOnline the first batch of data is expected by the end of September, with the study to be published later in the year.
She said: 'If we don't find anything, all we can conclude is if there is a link between periods and vaccines it is less common than the stdy can pick up.'
Dr Male said she was only able to recruit 250 women for her study because when she started looking for participants most had already been inoculated.
The participants come from countries
